The present invention relates to a ski boot comprising a first component, consisting essentially of a sole and an upper which encloses the foot and the malleolar region, and a second component consisting of a cuff which is articulated with respect to the upper so as to allow the cuff to move from front to rear and vice versa, and means for retaining the cuff which counteract the rearward tilting of the cuff but give way when the force tending to tilt the cuff exceeds a specific value.
The purpose of such a design is to protect the skier""s knee, and more precisely the anterior cruciate ligament, when an excessive forward force is exerted on the tibia relative to the femur. It has been observed that tears of the anterior cruciate ligament due to an excessive force of this type have become much more widespread while other types of injury, in particular broken legs and ankles have become much less frequent because of the progress made with safety bindings. Excessive force on the anterior cruciate ligament occurs, in particular, when going over a bump, either when jumping, on landing, or when going down the bump again quickly.
U.S. Pat. No. 5,107,608, the content of which is incorporated by reference, has already disclosed a boot equipped with a releasable retaining device intended to protect the anterior cruciate ligament in case of excessive force. This device comprises a latch in the form of a bent lever of the first class that is retained by a spring. In case of excessive force on the cuff, the spring will no longer be capable of retaining the latch, which will tilt and free the cuff. Such a device has the drawback that the skier cannot put it back into its initial position. It is also relatively bulky.
International Application WO 97/22 271, the content of which is incorporated by reference, moreover discloses a ski boot which is also equipped with a retaining device which releases in case of excessive force on the cuff, rearward. This device consists of a sprung linkage, the articulation of which has enough play to allow the articulation pin some degree of longitudinal movement in the lower element of the linkage, and the elements of which abut, at a point lying some distance from the articulation pin, at the end of a travel smaller than the possible displacement of the pin. Once the elements of the linkage have come to abut and the spring of the linkage has already undergone some degree of compression, if the force on the cuff continues to increase then the elements of the linkage will pivot about their bearing point and the linkage will release if its articulation moves beyond alignment of the points of articulation of the linkage to the upper and to the cuff. This device has the advantage that the skier can put it back into its initial position, but it is relatively complex and bulky.
U.S. Pat. No. 5,446,976 to Donnadieu et al, the content of which is herein incorporated by reference, describes a cross-country ski boot having a shell and a lower-leg cuff articulated with respect to each other. A compression spring 40 is interposed between the shell and the lower-leg cuff in a manner that allows a walking movement required for cross country skiing, while at the same time providing an xe2x80x9cenergy sourcexe2x80x9d causing an automatic liffing of the front end or spatula of the ski. FIG. 5 of Donnadieu shows a resilient deformable blade 61 that operates by buckling between a resting position and a working position, in order to provide this xe2x80x9cenergy sourcexe2x80x9d. Because this boot is designed for cross-country skiing, this blade must operate in the elastic range, just as a compression spring. Referring to FIG. 1 of the drawings, a normalized force vs displacement graph of a blade of this nature is shown. U is the normalized ultimate strength of the leaf. Elastic operation in the operating range requires that the inflection point A be low and that the curve segment B after the inflection point have characteristics of a compression spring (i.e., that displacement be roughly proportional to applied force). Therefore, because the inflection point A is passed in normal operation, the blade 61 has absolutely no safety function.
The object of the present invention is to produce retaining means which release when a force exceeds the normal operating limit, but have a much simpler design than the retaining means known from the prior art.
The boot according to the invention is one wherein the retaining means consist of a part that works in compression and gives way by buckling when a predetermined ultimate strength is reached.
The retaining part may be a part which recovers its shape, such as an elastic flexible leaf, or a part which does not recover its shape, such as a leaf or a bar whose buckling causes it to fold beyond the elastic limit or a tubular part which yields by being crushed beyond a certain axial compression, the common aspect being the limit at which the retaining part gives way.
In the case of a flexible leaf which recovers its shape, it could be connected to one of the components of the boot, preferably the cuff, by a clevis articulated to the cuff, so that it can occupy either a retaining position or a position away from the other component of the boot, allowing the cuff to be straightened up, that is to say a resting or walking position.